Description of the Pest
Soft scales are typically found on woody and foliage plants. The first nymphal instar is called a crawler and has functional legs, while the remaining instars are attached to the leaf or twig and (with the exception of green shield scale) do not move. These scales typically have a more conspicuous profile from the side view compared with armored scales and produce copious honeydew. The protective covering over a soft scale cannot be separated from its body. Brown soft scale adults are fairly flat in profile, range in color from yellowish green to brown, and are often spotted or mottled to uniform brown. Hemispherical scale adults are round, hard, brown, smooth and shiny. Black scale adults are globular and hardened with ridges on the back that look like the letter "H". Green shield scale, introduced into California in the early 1990s, has a light yellow-green color as an immature. Female green shield scales produce a mass of eggs in a cottony ovisac without mating (i.e., reproduction is parthenogenetic and there are no males).
Soft scales remove sap from plants and cause yellowing of leaves and overall plant decline. Green shield scale ovisacs and the honeydew excreted by all the soft scales disfigure plants. Honeydew allows the growth of black sooty mold fungi and attracts ants. Ants may then carry scales to uninfested plants as well as protect them from natural enemies such as predators and parasites.
The black scale parasite, Metaphycus helvolus, has also been used for control of the closely related hemispherical scale. The mealybug destroyer, Cryptolaemus montrouzieri, is known to be an effective predator of green shield scale. Green shield scale, however, is a CDFA "B" rated quarantine pest, so plant material must be entirely free of the scale to be shipped. For more information, see BIOLOGICAL CONTROL.
Exclusion of windblown crawlers can be accomplished by covering openings to the greenhouse with fine mesh screens. Prune out and discard heavily infested plant parts. Control ants.
Monitoring and Treatment Decisions
Visual inspection of plants will help locate infestations and may permit localized treatments of hot spots. The presence of ants climbing on the plant can also indicate a problem with scales. To monitor the crawler stage, place double-sided sticky tape around stems.
Treatment is generally warranted when scales are present. Optimum treatment timing is when crawlers are active; however, this can be difficult when there are overlapping, multiple generations. Multiple applications are generally necessary.
Selected Materials Registered for Use on Greenhouse or Nursery Ornamentals
Read and follow the instructions on the label before using any pesticide. Before using a pesticide for the first time or on a new crop or cultivar, treat a few plants and check for phytotoxicity. Also consider pesticide resistance management and environmental impact.
|Manufacturer||REI1||Mode of action2||Comments|
|Valent||12||7C||Do not apply more than 2 times per cropping cycle or per 6 months.|
|Wellmark||4||3||Apply prebloom. Also labeled for low volume use.|
|Cleary||12||4A||Apply as a
|OHP||12||4A||Not to be used more than once every 16 weeks. Do not apply to soils that are water logged or saturated. Do not apply to bedding plants intended to be used as food crops.|
|(Marathon 60 WP)||OHP||12||4A||As above. Apply only as a drench.|
extract of neem oil#
|OHP||4||un||Do not spray plants under stress. Target pest must be completely covered with spray. Check label for list of plants that can be treated. May cause injury to flowers.|
JMS Stylet Oil
|Use as above for neem oil. Also, do not use with sulfur fungicides; check label for tank mix restrictions.|
|Valent||24||1B||A number of chrysanthemum varieties have exhibited phytotoxic reactions. In greenhouses only labeled for use on anthurium, cacti, carnation, rose, orchids, some foliage plants, young poinsettia, and some varieties of chrysanthemum. Can stunt new growth in roses.|
(PT 1300 Orthene TR)
|Whitmire MicroGen||24||1B||An aerosol for greenhouse use only.|
|various||12||1B||Not for greenhouse use.|
|1||Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing.|
|2||Rotate chemicals with a different mode-of-action Group number, and do not use products with the same mode-of-action Group number more than twice per season to help prevent development of resistance. For example, the organophosphates have a Group number of 1B; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode of action Group numbers are assigned by IRAC (Insecticide Resistance Action Committee).|
|3||Note that single doses of soaps or oils can be used at anytime in a pesticide rotation scheme without negatively impacting resistance management programs.|
|4||Check with certifier to determine which products are organically acceptable.|
|*||Restricted use material. Permit required for purchase or use.|
|#||Acceptable for use on organically grown ornamentals.|